If you deleted the Payment Type and re-created to include the newly added classes, you will end up seeing duplicate invoices.
If you run in to this issue you will have to,
Below image explains how you can distinguish between the invoices generated by two different Payment Types
As soon as Payment Type is saved the current and future month invoices will appear on this tab.
You can filter the duration to see the past or future one month invoices.
As you can see the Aayid Shaikh got 150$ invoice instead of 350$, as it was added as exception to payment type.
From this point you can either manage the Receipts from Web portal or Ad-Din Mobile App.